The only time room temperature really plays a role is if you haul your amp from a really cold car into a relatively warm room, then you'll want to give it enough time to warm up to whatever temperature the room is before turning it on. We're talking going from thirty or forty degrees to seventy, which is a pretty large difference. For your situation, the temperature difference isn't all that great and shouldn't be a problem. Turn it on, leave it on standby for a couple of minutes, and by then the tubes will have warmed everything up just fine. Once you start playing it the temperature inside the amp is going to come up anyway.
